In computing systems, such as desktop computers, portable computers, personal digital assistants (PDAs), servers, and others, storage devices are used to store data and program instructions. One type of storage device is a disk-based device, such as magnetic disk drives (e.g., floppy disk drives or hard disk drives) and optical disk drives (e.g., CD or DVD drives). Such disk-based storage devices have a rotating storage medium with a relatively large storage capacity. However, disk-based storage devices offer relatively slow read-write speeds when compared to operating speeds of other components of a computing system, such as microprocessors and other semiconductor devices.
Another type of storage device is a solid state memory device, such as a dynamic random access memory (DRAM), static random access memory (SRAM), flash memory, and electrically erasable and programmable read-only memory (EEPROM). Although solid state memory devices offer relatively high read-write speeds, usually on the order of nanoseconds, they have relatively limited storage capacities.
With improvements in nanotechnology (technology involving microscopic moving parts), other types of storage devices are being developed. One such storage device is based on atomic force microscopy (AFM), in which one or more microscopic scanning probes are used to read and write to a storage medium. Typically, a scanning probe has a tip that is contacted to a surface of the storage medium. Storage of data in the storage medium is based on perturbations created by the tip of the probe in the surface of the storage medium. In one implementation, a perturbation is a dent in the storage medium surface, with a dent representing a logical “1,” and the lack of a dent representing a logical “0.” Other types of perturbations that can be created in the surface of the storage medium include creating or altering the topographic features or composition of the storage medium, altering the crystalline phase of the medium, filling or emptying existing electronic states of the medium, creating or altering domain structures or polarization states in the medium, creating or altering chemical bonds in the medium, employing the tunneling effects to move and remove atoms or charge to or from the medium, or storing/removing charge from a particular region.
Typically, for improved access speeds, multiple probes are used, with the multiple probes usually arranged in an array. The array of probes are scanned across the surface of a storage medium to detect for the presence or absence of perturbations to determine the states of corresponding bits of data. In storage devices that use dents to store data bits, the dents are formed by heating the probe tips and applying a downward force on the probes such that the dents are imprinted into the storage surface of the storage medium. For accurate operation, the probe array and the storage medium have to be aligned with respect to each other. Temperature changes and variations between the probe array and the storage medium may cause mis-alignment between previously recorded dents and the probes. For example, the probe array may have a different coefficient of thermal expansion than the storage medium. Thus, once heated, mis-alignment may cause some of the probes in the array to go off track. If this occurs, perturbations in the surface of the storage medium may be missed, which may cause the probes to erroneously detect that perturbations are not present. As a result, read errors may occur, which reduces reliability of storage device operation.